In recent years, devices, which treat picture information as digital data, which, in such a case, aim to transmit and store information with a high efficiency, and which adhere to a scheme, such as MPEG, for compressing picture information using orthogonal transformation, such as discrete cosine transformation, and using motion compensation by utilizing redundancy that is unique to the picture information have become widespread in both information distribution by broadcasting stations and information reception by ordinary homes.
In particular, MPEG2 (ISO/IEC 13818-2), which is defined as a general picture coding scheme, is a standard covering both interlaced scan pictures and progressive scan pictures, and standard resolution pictures and high-definition pictures, and is currently widely used in a wide variety of applications including professional applications and consumer applications. Using an MPEG2 compression scheme, for example, a coding rate (a bit rate) of 4 to 8 Mbps is assigned in a case of a standard-resolution interlaced scan picture having 720×480 pixels, and a coding rate of 18 to 22 Mbps is assigned in a case of a high-resolution interlaced scan picture having 1920×1088 pixels, whereby a high compression ratio and an excellent picture quality can be realized.
MPEG2 was mainly intended for high-picture-quality coding suitable for broadcasting, but was not compatible with a coding scheme for realizing a coding rate (a bit rate) lower than that determined in MPEG1, i.e., a higher compression ratio. It was considered that needs of such a coding scheme will increase in the future as mobile terminals become widespread, and an MPEG4 coding scheme was standardized for the increasing needs. Regarding a picture coding scheme, the specification of the scheme was approved as an ISO/IEC 14496-2 international standard in December, 1998.
Furthermore, in recent years, standardization of a standard called H. 26L (ITU-T Q6/16 VCEG), which originally aimed to code pictures that are used for teleconferences, has been in progress. It is known that, although H. 26L requires a larger amount of computation for coding and decoding the pictures, compared with a conventional coding scheme such as MPEG2 or MPEG4, a higher coding efficiency is realized with H. 26L. Additionally, currently, as part of MPEG4 activities, standardization for realizing a higher coding efficiency has been performed as Joint Model of Enhanced-Compression Video Coding on the basis of H. 26L by incorporating functions that are not supported in H. 26L. Regarding a schedule of standardization, an international standard called H. 264 and MPEG-4 Part 10 (Advanced Video Coding) was set in March, 2003.
FIG. 13 is a block diagram showing a schematic configuration of a picture information coding device 100 that outputs picture compression information based on the AVC standard.
The picture information coding device 100 includes an A/D converter unit 101, a screen rearrangement buffer 102, an adder 103, an orthogonal transformation unit 104, a quantization unit 105, a lossless coding unit 106, a storage buffer 107, a dequantization unit 108, an inverse orthogonal transformation unit 109, a deblocking filter 110, a frame memory 111, an intra-prediction unit 112, a motion prediction/compensation unit 113, a rate control unit 114, and so forth.
In the picture information coding device 100 shown in FIG. 13, the A/D converter unit 101 converts an input picture signal to a digital signal, and supplies the digital signal to the screen rearrangement buffer 102. Then, the screen rearrangement buffer 102 performs frame rearrangement in accordance with a group-of-pictures (GOP) structure of picture compression information that is to be output from the picture information coding device 100.
Here, regarding picture information on which intra-coding, i.e., coding using a single frame, is to be performed, difference information concerning the difference between input picture information and pixel values that are generated by the intra-prediction unit 112 is input to the orthogonal transformation unit 104. Then, the difference information is subjected to orthogonal transformation, such as discrete cosine transformation or Karhunen-Loeve transformation, by the orthogonal transformation unit 104. The orthogonal transformation unit 104 supplies a transformation coefficient that is obtained by orthogonal transformation to the quantization unit 105.
The quantization unit 105 performs a quantization process on the transformation coefficient that is supplied from the orthogonal transformation unit 104, and supplies the quantized transformation coefficient to the lossless coding unit 106.
The lossless coding unit 106 performs lossless coding, such as variable length coding or arithmetic coding, on the quantized transformation coefficient that is supplied from the quantization unit 105. The transformation coefficient that is lossless-coded by the lossless coding unit 106 is stored in the storage buffer 107, and output as the picture compression information.
The behavior of the quantization unit 105 is controlled by the rate control unit 114. Furthermore, the quantization unit 105 supplies the quantized transformation coefficient to the dequantization unit 108. Moreover, the quantized transformation coefficient is subjected to an inverse orthogonal transformation process by the inverse orthogonal transformation unit 109, thereby being transformed to decoded picture information. After the information is subjected to removal of block noise by the deblocking filter 110, the information is stored in the frame memory 111. Information concerning an intra-prediction mode that is applied to blocks/macro blocks in the intra-prediction unit 112 is transmitted to the lossless coding unit 106, and coded as a portion of header information in the picture compression information.
On the other hand, regarding picture information on which inter-coding, i.e., coding using a plurality of frames, is to be performed, picture information that is supplied from the screen rearrangement buffer 102 is input to the motion prediction/compensation unit 113. The motion prediction/compensation unit 113 reads, from the frame memory 111, picture information that is to be simultaneously referred to. The motion prediction/compensation unit 113 performs a motion prediction/compensation process to generate reference picture information, and supplies the reference picture information to the adder 103. The adder 103 transforms the picture information, which is supplied from the screen rearrangement buffer 102, to a difference signal representing the difference between the picture information and the reference picture information. The motion prediction/compensation unit 113 simultaneously supplies motion-vector information to the lossless coding unit 106. The lossless coding unit 106 performs a lossless coding process, such as variable length coding or arithmetic coding, on the motion-vector information, and forms information that is to be inserted into a header portion of picture compression information. The other processes are the same as the processes related to the picture compression information that is subjected to intra-coding.
FIG. 14 is a block diagram showing a schematic configuration of a picture information decoding device 200 that realizes picture compression using orthogonal transformation, such as discrete cosine transformation or Karhunen-Loeve transformation, and using motion compensation.
The picture information decoding device 200 includes a storage buffer 201, a lossless decoding unit 202, a dequantization unit 203, an inverse orthogonal transformation unit 204, an adder 205, a screen rearrangement buffer 206, a D/A converter unit 207, a frame memory 208, a motion prediction/compensation unit 209, an intra-prediction unit 210, a deblocking filter 211, and so forth.
In the picture information decoding device 200 shown in FIG. 14, the storage buffer 201 temporarily stores input picture compression information, and transfers the stored picture compression information to the lossless decoding unit 202. The lossless decoding unit 202 performs a process such as variable length decoding or arithmetic decoding on the picture compression information, which is transferred from the storage buffer 201, in accordance with a determined format of picture compression information. Furthermore, when a frame is an intra-coded frame, the lossless decoding unit 202 also decodes intra-prediction mode information that is stored in a header portion of the picture compression information, and supplies the information to the intra-prediction unit 210. Moreover, when the frame is an inter-coded frame, the lossless decoding unit 202 also decodes motion-vector information that is stored in the header portion of the picture compression information, and supplies the information to the motion prediction/compensation unit 209.
The dequantization unit 203 dequantizes a quantized transformation coefficient that is supplied from the lossless decoding unit 202, and supplies the transformation coefficient to the inverse orthogonal transformation unit 204 as a transformation coefficient. The inverse orthogonal transformation unit 204 performs, in accordance with a predetermined scheme, fourth-order inverse orthogonal transformation on the transformation coefficient that is supplied from the dequantization unit 203.
Here, when the frame is an intra-coded frame, picture information that has been subjected to an inverse orthogonal transformation process is supplied to the adder 205, and combined with prediction picture information that is generated by the intra-prediction unit 210. Furthermore, after the information is subjected to removal of block noise by the deblocking filter 211, the information is stored in the screen rearrangement buffer 206. The information is output after a D/A conversion process is performed by the D/A converter unit 207.
On the other hand, when the frame is an inter-coded frame, the motion prediction/compensation unit 209 generates reference picture information on the basis of the motion-vector information, which has been subjected to a lossless decoding process by the lossless decoding unit 202, and on the basis of picture information that is stored in the frame memory 208, and supplies the reference picture information to the adder 205. The adder 205 combines the reference picture information with an output of the inverse orthogonal transformation unit 204. The other processes are the same as the processes related to the intra-coded frame.
Examples of documents of the conventional art for the present application include Japanese Unexamined Patent Application Publication No. 2003-289544, Japanese Unexamined Patent Application Publication No. 2004-289808, Japanese Unexamined Patent Application Publication No. 2004-274732, Japanese Unexamined Patent Application Publication No. 2004-187264, Japanese Unexamined Patent Application Publication No. 2004-274694, and Japanese Unexamined Patent Application Publication No. 2006-129177.